Electric conductor



Nov. 23, 1943. P. E. H. EICHINGER ELECTRIC CONDUCTOR Filed March 6, 1959zaazzzz er hitherto in these Patented Nov. 23, 1943 UNITED STATES PATENT'oFF1c-E 2,334,756' Philippe EUIZZZOEFII: France;

vested in the Alien Property Custodian Application March 6, 1939, SerialNo. 260,226

a In France March 7, 1938 1 Claim.- 7 (01. 174-,-1o2') The presentinvention relates to the manufacture of electric wires, cables orconductors composed of one or a plurality of single. 01 dividedconducting or resistant cores which are insulated Irom a metal sheath'by a powdered mineral insulating material.

It has already been proposed, for manufacturing wires, cables andconductors of this category, in particular when the finished product isobtained by elongationof. a suitably dimensioned rough shape, to use amineral insulating material in the highly compact and totally dehydratedstate.

The insulating material usually employed manufactures is ordinarymagnesium oxide.

The applicant has proved that the. hitherto employed insulatingmaterials, in particular or.-

dinary magnesium oxide in uncompacted form,

do not possess any natural dielectric strength and the breakdown voltageof the conductors they serve to form is of the same order of magnitudeas it the insulating layer were replaced by air.

In fact, the breakdown voltage is, on an average, about 3,000 volts whenthe thickness of the insulating material is 1.5 mm. and 4,500 volts whenthe thickness reaches 3 mm., etc.

Now, these are precisely the breakdown voltages of conductors composedof a cylindrical core and of a likewise cylindrical outer sheath whichare separated by air, the constant distance between the two armatures ofthe condenser thus formed being, according to cases, respectively 1.5mm., 3 mm., etc.

It would therefore appear that, in these conductors, everything takesplace as though the purpose of the insulating material employed was todefine. and ensure the. geometrical position of the core in thetransverse section of the sheath, without increasing the dielectricstrength of the conductor. I 1

The drawing illustrates a cross section of a conductor made inaccordance with the present invention.

The present invention provides a very conuncompacted insulating materialused naturally possesses a property of dielectric strength that is onlyequal to that or air.

For this purpose, during its manufacturing process, the conductor willbe subjected to a treatment of such a nature as to allow per-' manentpressures to subsist in the insulating material which substantiallyincrease its dielectric strength.

Research work done by the applicant has shown him that the dielectricstrength of a powdered mineral insulating material is, to a certainextent, proportional to the value of the pressures which -may occurbetween the particles of the insulating material. Now, for a conductorwhich is in the process of manufacture and at a certain phase ofdrawing, such pressures vary within wide limits, according to whetherthe metal of the sheath is in the coldhammered state or whether on thecontrary it has just been annealed.

It will in fact be understood that, everything being equal, saidpressures of the insulating material are greatest when the conductor hasjust undergone the final drawing operation'durin which it has reachedits final dimensions, since economy is naturally an incentive tocontinueplaced in position and installed. I

siderable improvement in the processes for man- I uiacturing conductorsof this category.

Said invention consists in imparting to the insulating material by anappropriate treatment, a property of dielectric strength which it doesriot naturally possess and which will hereinafter be called extrinsicdielectric strength, so that the conductor will be characterized by ahigher breakdown voltage than that of air, even if the By annealing theconductor, the insulating material will lose the state of pressure inwhich it was,- and its extrinsic dielectric strength will disappear withit.

Now, the applicant has proved that the state of pressure ofthe-insulating material varies to a very. slight extent between theinstant when a conductor which has been annealed is' subjected forexample to a very slight pass even without elongation of the roughshape, and the instant when, on the contrary, drawing. iscontinued up tothe limit beyond which a break would be produced.

Thus, if the sheath of a previously drawn and annealed conductor is'very slightly" cold-ham- Jmered or shaped, i'or example by anappropriateadditional pass, in such a manner as not to exceed for example Sjifofthe total elongation" 2 01 the metal, it is found that the resilientpressure or the insulating material has returned to very substantiallyits maximumvalue, and'with it has realized its highest extrinsicdielectric strength, although the conductor can still undergo 95% oiitselongation and consequently, in

practice, still leaves the conductor itself with all 1 its mechanicalflexibility;

It is an easy matter in practice to ascertain the extent of saidadditional pass. It may be said that it can ,be chosen in such a manneras to properties and in particular its "shape" the sheath until theinstant-when. the

insulating material reaches the limiting pressure (defined in FrenchPatent No. 795,277) that is to say until the instant when a moreconsiderable pass, however small it may be, would cause the same sampleof conductor which has beensubjected to an annealing treatment only.

In a practical example, a conductor of about 5.3. mm. outside diameteror sheath and having I an insulating layer of about 1.5 mm. thicknessmade of a mineral with no property of intrinsic dielectric rigidity,ordinary magnesium'oxideior example, is characterized by a breakdownvoltage of about 3,000 volts, after the last annealing operation of theseries or metallurgical treatments of the manufacture and ii the processJust described is not applied. If, on the contrary, a very slightshaping is eflected, for example by a drawing operation which reducesthe outside diameter of the sheath to, 5.2, the breakdown voltage of thesame conductor becomes higher than 4,000 volts.

Of cOurse the invention applies whatever be the number of cores of theconductor, the metal which they and the sheath are made of and theparticular refractory powdered insulating material used. Said inventioncovers, by way oi new industrial products, conductors of the abovementioned category wherein the dielectric rigid property of extrinsicdielectric strength and in particularly the use, for the manufacture ofthe.

electric conductors in question and whatever he the process employed forcarrying it out, of the method of operation of shaping the sheath, whichmethod is characterized by the fact that the metals of the sheath and ofthe core have both retained almost their entire capacity of coldhammering and even of their property or elongation,

and by the further fact that the dielectric strength of the insulating"material of the conductor in the latter state considered is at leastity is at least 20% greater than the rigidityof the same conductor whichhas ing only.

Iclaim:

An electric conductor'comprising at least one condueting core, ametallic sheath and powdered min'eral insulating material interposedbetween said core and sheath, the said insulating material being under apressure 01' such magnitude that its dielectric strength is at least 20%greater than the dielectric strength would be in the absence ofpressure, said conductor being capable of elongation withoutrupture u to95% of the elongation of which it would be capable in the absonceofpressure, and possessing substantially the ca- 20% greater than thedielectric rigidity of the pacity for being bent which is characteristicof the conductor in annealed state;

emu EU ENE mm mcnmonaf undergone anneal-

